1. Field of the Invention
In fuel injection devices with fillable high-pressure collection chambers (common rails), injectors are used that can be subjected constantly to the extremely high system pressure, which on the one hand enables a largely delay-free injection of fuel, but on the other requires the prevention of even the least after-injections after the end of injection by means of a rapidly effected needle closure at the end of injection.
2. Description of the Prior Art
European Patent Disclosure EP 0 657 642 A2 relates to a fuel injection device for internal combustion engines. A high-pressure collection chamber (common rail) communicates constantly with the injection valves. To prevent the high system pressure from being applied constantly to the injection valves, the control valve is designed such that during the intervals between injections, it closes the communication of the injection component with the pressure reservoir and opens up a communication between the injection valve and a relief chamber. As a result, the closing forces to be exerted, which are brought to bear by spring forces, can be reduced. Increasingly stringent demands with regard to the level of the system pressure require higher closing forces, which necessitate springs that are dimensioned differently. The installation space available for the movable springs, however, is limited.
German Patent Disclosure DE 197 01 879 A1 also relates to a fuel injection device for internal combustion engines. By means of a triggerable magnet valve, a relief conduit, discharging into a work chamber that is under pressure, can be opened in such a way that the control valve can be moved into an opening or a closing position.
With the throttle element provided on the control part, it is possible, without having to turn to additionally required components or helical springs that generate greater closing forces, to achieve an increase in the closing force acting on the control part. This assures both faster closure of the nozzle needle at the end of injection and a tighter closure of the high-pressure collection chamber from the high-pressure collection supply line. Increasing the closing force at the control part prevents the occurrence of after-injections of even the tiniest fuel quantities, by increasing the pressure at the spring chamber. During the injection event, the spring chamber, with a spring element let into it, is subjected to the fuel, which is under high injection pressure. The pressure relief line provided next to the control part is closed by the control edges of the control part, so that during the injection, the high fuel pressure also prevails at the spring chamber and as a function of the opening time of the control part in the spring chamber, a fuel pressure builds up that promotes the process of restoration of the control part after the end of injection.
Opposite the control part, in its sleeve surrounding it, there is a further throttle element, which is provided in the pressure-free relief line. After the end of the injection event, the throttle in the relief line prevents cavitation from occurring in the injection nozzle. With appropriate dimensioning of the cross section of the throttle element, the spring chamber can on the one hand be completely pressure-relieved, and on the other a complete pressure relief of the spring chamber can be prevented by providing that by suitable dimensioning of the cross section of the throttle element, an increased residual pressure in the spring chamber can be preset and continue to be maintained.
Another advantage that can be attained with the provisions of the invention is that before the engine is first started, venting of the engine is attainable by means of the throttle element at the control part of the 3/2-way valve.
The effect of the provisions of the invention that is significant for the functional reliability of injection valves resides in a pressure equalization, effected via the throttle element, that is gradually established at the nozzle needle on the one hand and the spring chamber on the other through the throttle element and the bore, if malfunctions occur at the injection valve, for instance because a magnet valve has not closed or because of seizure or friction of the control part at its seat. The pressure equalization is established within a period of time. The available period of time for the pressure equalization via the cross section of the throttle element determines the maximum injection quantity at maximal system pressure. The maximum injection quantity, which exceeds the rated injection quantity, can be deflected, by suitable dimensioning of the cross section of the throttle element in the control part, in such a way that the engine will not suffer any damage if an injection event at the maximum injection quantity occurs.
With the thus mechanically controlled maximum injection quantity, electronic malfunctions in the form of missing or overly long trigger signals can also be compensated for.